The floor starts to sway. The windows rattle. Your heartbeat quickens. They’re the telltale signs of an earthquake, and here in northeastern Japan we felt them as recently as February, when a magnitude 7.3 tremor struck off the Pacific coast and injured more than 100 people. Seismologists said it was an aftershock from the massive quake that shattered the region adecade earlier, with its accompanying tsunami leaving 15,899 dead and 2,527 missing.